Add Enterprise Server 3.26.9 release notes

Author: ainoam

docs/release_notes/clearml_server/enterprise/ver_3_26.md

@@ -3,6 +3,12 @@ title: Version 3.26
 ---
 
 
+### Enterprise Server 3.26.9
+
+**Bug Fixes**
+* Fix users sometimes automatically logged out immediately upon SSO re-login after inactivity
+* Various security fixes
+
 ### Enterprise Server 3.26.8 
 
 * Improve SSO security